Journal articles: 'Crustal anomalies'

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Raymond, Carol A., and Richard J. Blakely. "Crustal magnetic anomalies." Reviews of Geophysics 33 (1995): 177. http://dx.doi.org/10.1029/95rg00444.

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Filho, Nelson Ribeiro, Cristiano Mendel Martins, and Renata de Sena Santos. "A NOVEL REGIONAL-RESIDUAL SEPARATION APPROACH FOR GRAVITY DATA THROUGH CRUSTAL MODELING." Revista Brasileira de Geofísica 36, no. 4 (December 21, 2018): 1. http://dx.doi.org/10.22564/rbgf.v36i4.1980.

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ABSTRACT. Gravity anomalies normally contain information of all sources beneath Earth’s surface. Once residual anomalies exhibit information about the main target, the knowledge of this specific residual signal is extremely important to interpretation. To find this signal, it’s necessary to perform regional-residual separation. We present here a new approach of separation by using gravity crustal modeling. We divide the surface in prisms, with density given by GEMMA. We calculate the regional signal, assuming Earth’s crust can be the source of observed anomaly. This methodology was applied on Barreirinhas basin-Brazil. Its formation is related to geologic events in South America-Africa break. Besides, the complex geology is the main obstacle on finding the residual anomaly. We compare our methodology with robust-polynomial fitting and spectral-analysis. They were not able to identify the residual anomaly. Main trouble relies on absence of crust information. Those kind of environment usually requires forward modeling and/or gravity inversion. On the other hand, our approach considers all crust’s parameters. Then the difficulty on choosing the residual no longer exists. The residual anomaly follows a geologic pattern. The crustal depocenter was mapped between structural faults. Therefore, our results satisfies the main expectation and are extremely linked to Barreirinhas basin’s geological background. We recommend this separation procedure, once Earth’s crustal model and gravity data are available for all planet.Keywords: Gravity modeling; GEMMA model; Barreirinhas basin; residual anomaly. RESUMO. Anomalias gravimétricas contêm informações de todas as fontes na superfície terrestre. Uma vez que anomalias residuais exibem informações sobre alvos principais, o conhecimento desse específico sinal residual é extremamente importante para interpretação. Para encontrá-lo, é necessário realizar separação regional-residual. Apresentamos aqui uma nova abordagem de separação utilizando a modelagem gravimétrica crustal. Discretizamos a superfície em prismas, com densidade fornecida pelo modelo GEMMA. Calculamos o sinal regional, assumindo que a crosta terrestre é a fonte da anomalia observada. Aplicamos esta metodologia na bacia de Barreirinhas - Brasil, que tem sua formação relacionada aos eventos geológicos de separação da América do Sul e África. Além disso, a complexidade geológica é considerada o principal obstáculo para encontrar esta anomalia residual. Comparamos nossa metodologia com Ajuste Polinomial Robusto e Análise Espectral. Essas técnicas não foram capazes de identificar a anomalia residual. O principal problema se dá pela ausência de informações acerca da crosta. Para esse ambiente, geralmente requer modelagem direta e/ou inversão geofísica. Por outro lado, nossa abordagem considera todos os parâmetros crustais e a dificuldade em escolher o residual deixa de existir. A anomalia residual apresenta um padrão geológico. O depocentro crustal foi mapeado entre falhas estruturais. Nossos resultados satisfazem a expectativa principal e estão extremamente ligados ao cenário geológico da bacia. Recomendamos este procedimento de separação, uma vez que os modelos crustais e dados gravimétricos estão disponíveis para todo o planeta.Palavras-chave: Modelagem gravimétrica; modelo GEMMA; bacia de Barreirinhas; anomalia residual

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Phillips, Jeffrey D., Richard L. Reynolds, and Herbert Frey. "CRUSTAL STRUCTURE INTERPRETED FROM MAGNETIC ANOMALIES." Reviews of Geophysics 29, S1 (January 1991): 416–27. http://dx.doi.org/10.1002/rog.1991.29.s1.416.

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Zheng, Shuo, Kai Qin, Lixin Wu, Yanfei An, Qifeng Yin, and Chunkit Lai. "Hydrothermal anomalies of the Earth's surface and crustal seismicity related to Ms8.0 Wenchuan EQ." Natural Hazards 104, no. 3 (August 31, 2020): 2097–114. http://dx.doi.org/10.1007/s11069-020-04263-7.

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Abstract Hydrothermal anomalies related to the Ms8.0 Wenchuan earthquake (EQ) on May 12, 2009, have been widely reported. However, the reported anomalies have not been associated with multi-geosphere analysis, and space–time analysis with crustal seismicity is lacking. In this paper, the space–time variation of hydrothermal parameters, including soil moisture, soil temperature, near-surface relative humidity (RHsig995) and air temperature (TMPsfc), was first extracted and analyzed with the NCEP-FNL reanalysis dataset. The b-value (a seismic parameter from the Gutenberg–Richter law) was calculated and mapped to unravel the crustal stress and rock rupture. Our results reveal a similar time window for hydrothermal anomalies on April 20 and April 30, 2008, and these anomalies are mainly distributed along the southern and middle parts of the Longmenshan fault zone. The surface temperature anomalies lag behind the humidity anomalies, and the accelerating stress accumulation started since June 2007 and lasted for eight to nine months before the mainshock. The b-value mapping shows a segmented difference along strike of the Longmenshan fault, and that regional stress accumulated mainly in the southern parts of the F2 and F3 faults. We propose the occurrence of a complex coupling process led by crustal stress buildup before the Wenchuan EQ. The anomalies are concentrated in the southern part of the surface rupture zone. The prolonged crustal stress accumulation corresponds to the short intermittent hydrothermal response on the Earth’s surface before the Wenchuan EQ. Our findings reveal new hydrothermal anomalies in the Earth’s surface and atmosphere and explore direct link with seismogenic processes in the crust.

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Tang, Ming, Wei-Qiang Ji, Xu Chu, Anbin Wu, and Chen Chen. "Reconstructing crustal thickness evolution from europium anomalies in detrital zircons." Geology 49, no. 1 (September 4, 2020): 76–80. http://dx.doi.org/10.1130/g47745.1.

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Abstract A new data compilation shows that in intermediate to felsic rocks, zircon Eu/Eu* [chondrite normalized Eu/ ] correlates with whole rock La/Yb, which has been be used to infer crustal thickness. The resultant positive correlation between zircon Eu/Eu* and crustal thickness can be explained by two processes favored during high-pressure differentiation: (1) supression of plagioclase and (2) endogenic oxidation of Eu2+ due to garnet fractionation. Here we calibrate a crustal thickness proxy based on Eu anomalies in zircons. The Eu/Eu*-in-zircon proxy makes it possible to reconstruct crustal thickness evolution in magmatic arcs and orogens using detrital zircons. To evaluate this new proxy, we analyzed detrital zircons separated from modern river sands in the Gangdese belt, southern Tibet. Our results reveal two episodes of crustal thickening (to 60–70 km) since the Cretaceous. The first thickening event occurred at 90–70 Ma, and the second at 50–30 Ma following Eurasia-India collision. These findings are temporally consistent with contractional deformation of sedimentary strata in southern Tibet.

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Oran, Rona, Benjamin P. Weiss, Yuri Shprits, Katarina Miljković, and Gábor Tóth. "Was the moon magnetized by impact plasmas?" Science Advances 6, no. 40 (October 2020): eabb1475. http://dx.doi.org/10.1126/sciadv.abb1475.

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The crusts of the Moon, Mercury, and many meteorite parent bodies are magnetized. Although the magnetizing field is commonly attributed to that of an ancient core dynamo, a longstanding hypothesized alternative is amplification of the interplanetary magnetic field and induced crustal field by plasmas generated by meteoroid impacts. Here, we use magnetohydrodynamic and impact simulations and analytic relationships to demonstrate that although impact plasmas can transiently enhance the field inside the Moon, the resulting fields are at least three orders of magnitude too weak to explain lunar crustal magnetic anomalies. This leaves a core dynamo as the only plausible source of most magnetization on the Moon.

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Zheng, Ying, and Jafar Arkani-Hamed. "Joint inversion of gravity and magnetic anomalies of eastern Canada." Canadian Journal of Earth Sciences 35, no. 7 (July 1, 1998): 832–53. http://dx.doi.org/10.1139/e98-035.

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The power spectra and degree correlation of the surface topography and free-air gravity anomalies of eastern Canada show that the gravity anomalies are subdivided into three parts. The short-wavelength components (30-170 km, shorter than 30 km are not well resolved) largely arise from density perturbations in the crust and to a lesser extent from the surface topography and Moho undulation, whereas the contribution of intracrustal sources to the intermediate-wavelength components (170-385 km) is comparable with that of the topography. The long-wavelength components (385-1536 km) are overcompensated at the Moho. We present a crustal model for the intermediate- and long-wavelength components which takes into account the surface topography, density perturbations in the crust, and Moho undulation with a certain degree of isostatic compensation. The general characteristics of this model resemble the crustal structure revealed from seismic measurements. The reduced-to-pole magnetic anomalies of eastern Canada show no pronounced correlation with the topography and with the vertical gradient of the gravity anomalies, suggesting that the source bodies are within the crust and Poisson's relationship does not hold over the entire area. Assuming that the magnetic anomalies arise from induced magnetization, lateral variations of magnetic susceptibility of the crust are determined while taking into account the effects of the surface topography and the Moho undulation of our crustal model. The intermediate- and long-wavelength components of the susceptibility contrasts delineate major collision zones as low-susceptibility regions. We interpret this in terms of thermal demagnetization of the high-magnetic crustal roots beneath the collision zones.

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Saleh, Salah, Oya Pamukçu, and Ladislav Brimich. "The major tectonic boundaries of the Northern Red Sea rift, Egypt derived from geophysical data analysis." Contributions to Geophysics and Geodesy 47, no. 3 (September 1, 2017): 149–99. http://dx.doi.org/10.1515/congeo-2017-0010.

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AbstractIn the present study, we have attempted to map the plate boundary between Arabia and Africa at the Northern Red Sea rift region including the Suez rift, Gulf of Aqaba-Dead Sea transform and southeastern Mediterranean region by using gravity data analysis. In the boundary analysis method which was used; low-pass filtered gravity anomalies of the Northern Red Sea rift region were computed. Different crustal types and thicknesses, sediment thicknesses and different heat flow anomalies were evaluated. According to the results, there are six subzones (crustal blocks) separated from each other by tectonic plate boundaries and/or lineaments. It seems that these tectonic boundaries reveal complex structural lineaments, which are mostly influenced by a predominant set of NNW–SSE to NW–SE trending lineaments bordering the Red Sea and Suez rift regions. On the other side, the E–W and N–S to NNE–SSW trended lineaments bordering the South-eastern Mediterranean, Northern Sinai and Aqaba-Dead Sea transform regions, respectively. The analysis of the low pass filtered Bouguer anomaly maps reveals that the positive regional anomaly over both the Red Sea rift and South-eastern Mediterranean basin subzones are considered to be caused by the high density of the oceanic crust and/or the anomalous upper mantle structures beneath these regions whereas, the broad medium anomalies along the western half of Central Sinai with the Suez rift and the Eastern Desert subzones are attributed to low-density sediments of the Suez rift and/or the thick upper continental crustal thickness below these zones. There are observable negative anomalies over the Northern Arabia subzone, particularly in the areas covered by Cenozoic volcanics. These negative anomalies may be attributed to both the low densities of the surface volcanics and/or to a very thick upper continental crust. On the contrary, the negative anomaly which belongs to the Gulf of Aqaba-Dead Sea transform zone is due to crustal thickening (with limited heat flow values) below this region. Additionally in this study, the crustal thinning was investigated with heat flow, magnetic and free air gravity anomalies in the Northern Red Sea rift region. In fact, the crustal thinning of the study area was also proportional to the regions of observable high heat flow values. Finally, our results were found to be well correlated with the topography, free air, aeromagnetic and heat flow dataset profiles crossing most of the study area.

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Halekas, J. S., D. A. Brain, R. P. Lin, and D. L. Mitchell. "Solar wind interaction with lunar crustal magnetic anomalies." Advances in Space Research 41, no. 8 (January 2008): 1319–24. http://dx.doi.org/10.1016/j.asr.2007.04.003.

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Riad, Samir, and Hassan A. El Etr. "Bouguer anomalies and lithosphere-crustal thickness in Uganda." Journal of Geodynamics 3, no. 1-2 (July 1985): 169–86. http://dx.doi.org/10.1016/0264-3707(85)90027-4.

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Geiger, Hugh D., and Frederick A. Cook. "Analyses of crustal structure from bandpass and directionally filtered potential-field data: an example from western Canada." Canadian Journal of Earth Sciences 38, no. 6 (June 1, 2001): 953–61. http://dx.doi.org/10.1139/e00-109.

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Application of bandpass and directional filtering to potential-field data in northwestern Canada allows separation of anomalies due to northwest-oriented upper crustal sources that are associated with Cordilleran structures from anomalies due to northeast-oriented lower crustal sources that are primarily associated with Precambrian Shield rocks. In northeastern British Columbia, northeast-trending lower crustal structures of the Canadian Shield as represented in the gravity patterns appear to project west of the Tintina fault Northern Rocky Mountain Trench at about 56°N. About 400500 km farther north, the Tintina fault may penetrate into the lithospheric mantle. It is, thus, likely that the depth extent of the Tintina fault rises southward into the crust, as dextral strike-slip motion is transformed into contractional structures of the southern Cordillera.

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Wu, Guochao, Fausto Ferraccioli, Wenna Zhou, Yuan Yuan, Jinyao Gao, and Gang Tian. "Tectonic Implications for the Gamburtsev Subglacial Mountains, East Antarctica, from Airborne Gravity and Magnetic Data." Remote Sensing 15, no. 2 (January 4, 2023): 306. http://dx.doi.org/10.3390/rs15020306.

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The Gamburtsev Subglacial Mountains (GSMs) in interior East Antarctic Craton are entirely buried under the massive ice sheet, with a ~50–60 km thick crust and ~200 km thick lithosphere, but little is known of the crustal structure and uplift mechanism. Here, we use airborne gravity and aeromagnetic anomalies for characteristic analysis and inverse calculations. The gravity and magnetic images show three distinct geophysical domains. Based on the gravity anomalies, a dense lower crustal root is inferred to underlie the GSMs, which may have been formed by underplating during the continental collision of Antarctica and India. The high frequency linear magnetic characteristics parallel to the suture zone suggest that the upper crustal architecture is dominated by thrusts, consisting of a large transpressional fault system with a trailing contractional imbricate fan. A 2D model along the seismic profile is created to investigate the crustal architecture of the GSMs with the aid of depth to magnetic source estimates. Combined with the calculated crustal geometry and physical properties and the geological background of East Antarctica, a new evolutionary model is proposed, suggesting that the GSMs have been a part of the Pan-African advancing accretionary orogen superimposed on the Precambrian basement.

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Lai, Zhibin, Jiangqin Chao, Zhifang Zhao, Mingchun Wen, Haiying Yang, Wang Chai, Yuan Yao, Xin Zhao, Qi Chen, and Jianyu Liu. "Relationship between Crustal Deformation and Thermal Anomalies in the 2022 Ninglang Ms 5.5 Earthquake in China: Clues from InSAR and RST." Remote Sensing 15, no. 5 (February 25, 2023): 1271. http://dx.doi.org/10.3390/rs15051271.

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On 2 January 2022, an earthquake of Ms 5.5 occurred in Ninglang County, Lijiang City, the earthquake-prone area of northwestern Yunnan. Whether this earthquake caused significant deformation and thermal anomalies and whether there is a relationship between them needs further investigation. Currently, multi-source remote sensing technology has become a powerful tool for long-time-series monitoring of earthquakes and active ruptures which mainly focuses on single crustal deformation and thermal anomaly. This study aims to reveal the crustal deformation and thermal anomaly characteristics of the Ninglang earthquake by using both Interferometric Synthetic Aperture Radar (InSAR) and Robust Satellite Techniques (RST). First, Sentinel-1A satellite SAR data were selected to obtain the coseismic deformation field based on Differential InSAR (D-InSAR), and the Small Baseline Set InSAR (SBAS-InSAR) technique was exploited to invert the pre- and post-earthquake displacement sequences. Then, RST was used to extract the thermal anomalies before and after the earthquake by using Moderate Resolution Imaging Spectroradiometer Land Surface Temperature (MODIS LST). The results indicate that the seismic crustal deformation is dominated by subsidence, with 23 thermal anomalies before and after the earthquake. It is speculated that the Yongning Fault in the deformation area is the main seismogenic fault of the Ninglang earthquake, which is dominated by positive fault dip-slip motion. Meanwhile, the seismic fault system composed of NE- and NW-oriented faults is an important factor in the formation of thermal anomalies, which are accompanied by changes in stress at different stages before and after the earthquake. Moreover, the crustal deformation and seismic thermal anomalies are correlated in time and space, and the active rupture activities in the region produce deformation accompanied by changes in thermal radiation. This study provides clues from remote sensing observations for analyzing the Ninglang earthquake and provides a reference for the joint application of InSAR and RST for earthquake monitoring.

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Pajunpää, K., I. Lahti, B. Olafsdottir, and T. Korja. "Crustal conductivity anomalies in central Sweden and southwestern Finland." Geophysical Journal International 150, no. 3 (September 2002): 695–705. http://dx.doi.org/10.1046/j.1365-246x.2002.01740.x.

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Ferré, Eric C., Fatíma Martín-Hernández, Michael Purucker, and David A. Clark. "Thematic issue: Crustal and mantle sources of magnetic anomalies." Tectonophysics 624-625 (June 2014): 1–2. http://dx.doi.org/10.1016/j.tecto.2014.04.001.

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Jackson, Andrew. "Studies of crustal magnetic anomalies of the British Isles." Astronomy & Geophysics 48, no. 2 (April 2007): 2.09–2.13. http://dx.doi.org/10.1111/j.1468-4004.2007.48209.x.

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Zeng, Hualin, Qinghe Zhang, Yishi Li, and Jun Liu. "Crustal structure inferred from gravity anomalies in South China." Tectonophysics 283, no. 1-4 (December 1997): 189–203. http://dx.doi.org/10.1016/s0040-1951(97)00153-4.

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Lee, M. K., T. C. Pharaoh, J. P. Williamson, C. A. Green, and W. De Vos. "Evidence on the deep structure of the Anglo-Brabant Massif from gravity and magnetic data." Geological Magazine 130, no. 5 (September 1993): 575–82. http://dx.doi.org/10.1017/s0016756800020872.

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AbstractGravity and aeromagnetic data from Britain, Belgium and the southern North Sea have been compiled to provide coverage of the greater part of the Anglo-Brabant Massif. Colour pseudo-relief maps of the gravity and magnetic fields highlight important anomalies and trends which provide new information on the structure of the massif and its margins. Within the massif, prominent SSE-trending geophysical lineaments define the margins of distinctive blocks within the upper crust. These are cross-cut on the northeastern margin of the massif by prominent ESE- and SE-trending magnetic and gravity lineaments. The possible history and origin of the more prominent geophysical anomalies and lineaments are considered. Integrated modelling of the potential field data has been carried out along the BIRPS MOBIL-7 seismic reflection line to provide an interpretation of crustal structure across the northeast margin of the massif constrained by all three datasets. The principal features of the model are a non-reflective, non-magnetic upper crust, interpreted as the Caledonian fold–thrust belt, overlying a heterogeneous middle–lower crust with laterally varying reflectivity, magnetization and density. ESE-trending magnetic anomalies along the northeast edge of the massif are explained in terms of an irregular mid-crustal magnetic layer with a susceptibility comparable to that of the Tubize Group in the Brabant Massif. The top of this body is coincident with prominent dipping mid-crustal reflectors observed on the seismic reflection profile and its overall geometry is compatible with mid-crustal imbrication inferred from the seismic data.

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Arkani‐Hamed, J., and W. J. Hinze. "Limitations of the long‐wavelength components of the North American magnetic anomaly map." GEOPHYSICS 55, no. 12 (December 1990): 1577–88. http://dx.doi.org/10.1190/1.1442809.

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The magnetic anomaly map of North America and its related data set provide the opportunity not only to view the obvious short‐wavelength anomalies (<300 km) in a continental context, but to isolate and analyze the longer wavelength anomalies. However, care must be used in analyzing the longer wavelengths because of the effects of noncrustal sources on these anomalies. Inversion of the anomalies into lateral variations of crustal magnetization suggests that the long‐wavelength anomalies (>2600 km) are strongly affected by core field components that have not been completely removed from the North American data set. Furthermore, the piecewise matching of the magnetic anomalies of adjacent survey areas in the map compilation has contaminated the intermediate wavelength anomalies (300–2600 km).

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Strack, K. ‐M, E. Lüschen, and A. W. Kötz. "Long‐offset transient electromagnetic (LOTEM) depth soundings applied to crustal studies in the Black Forest and Swabian Alb, Federal Republic of Germany." GEOPHYSICS 55, no. 7 (July 1990): 834–42. http://dx.doi.org/10.1190/1.1442897.

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The long‐offset transient electromagnetics (LOTEM) sounding method is a valuable complementary technique for deep seismic exploration as applied to earth crustal investigations. During 1986, two LOTEM surveys were conducted to augment completed seismic investigations for crustal studies in southern West Germany, east of the Rhine graben. Our studies were motivated by the geoscientific activities within the framework of the German Continental Deep Drilling (KTB) project. The survey objectives were (1) to determine the applicability of the LOTEM method to crustal geophysics, (2) to investigate the correlation of resistivity anomalies with velocity anomalies, and (3) to confirm the method and interpretation in an area of known geology with existing geophysical data. The Black Forest and the Urach geothermal area survey results exhibit conductive features in the upper 10 km of the crust which were not previously defined by other geophysical data. Importantly, the results demonstrate a very strong correlation of a low‐velocity zone with low electrical resistivity at 5 to 7 km depth within the crystalline basement at both locations.

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van Wijk, Jolante W., Samuel P. Heyman, Gary J. Axen, and Patricia Persaud. "Nature of the crust in the northern Gulf of California and Salton Trough." Geosphere 15, no. 5 (August 14, 2019): 1598–616. http://dx.doi.org/10.1130/ges02082.1.

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Abstract In the southern Gulf of California, the generation of new oceanic crust has resulted in linear magnetic anomalies and seafloor bathymetry that are characteristic of active seafloor-spreading systems. In the northern Gulf of California and the onshore (southeastern California, USA) Salton Trough region, a thick sedimentary package overlies the crystalline crust, masking its nature, and linear magnetic anomalies are absent. We use potential-field data and a geotherm analysis to constrain the composition of the crust (oceanic or continental) and develop a conceptual model for rifting. Gravity anomalies in the northern Gulf of California and Salton Trough are best fit with crustal densities that correspond to continental crust, and the fit is not as good if densities representative of mafic rocks, i.e., oceanic crust or mafic underplating, are assumed. Because extensive mafic underplated bodies would produce gravity anomalies that are not in agreement with observed gravity data, we propose, following earlier work, that the anomalies might be due to serpentinized peridotite bodies such as found at magma-poor rifted margins. The density and seismic velocities of such serpentinized peridotite bodies are in agreement with observed gravity and seismic velocities. Our conceptual model for the Salton Trough and northern Gulf of California shows that net crustal thinning here is limited because new crust is formed rapidly from sediment deposition. As a result, continental breakup may be delayed.

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Kim, Jeong Woo, Ralph R. B. von Frese, and Hyung Rae Kim. "Crustal modeling from spectrally correlated free‐air and terrain gravity data—A case study of Ohio." GEOPHYSICS 65, no. 4 (July 2000): 1057–69. http://dx.doi.org/10.1190/1.1444799.

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We investigate the use of spectral correlation theory to analyze terrain gravity effects and free‐air gravity anomalies of Ohio for possible constraints on the thickness variations and neotectonics of the crust. Terrain gravity effects are computed from the topography by Gauss‐Legendre quadrature integration and are compared against independent free‐air gravity anomaly observations for their wavenumber correlation spectrum. Spectral correlation filters are designed accordingly to extract terrain‐correlated free‐air gravity anomalies that are subtracted from the terrain gravity effects for estimates of the compensated terrain gravity effects. These effects are used to model the Moho by inversion, assuming they predominantly reflect crustal thickness variations. Our results characterize the middle third of Ohio as a broad zone of thickened Precambrian crust, which also may include rifted regions where the thickness of the prerift crust has been reduced greatly. Furthermore, we find that about 83% of the instrumentally determined earthquake epicenters are located within the inferred thinner regions of Ohio’s crust or at their margins where compressional stresses may dominate. In general, these crustal thickness variations provide new constraints on modeling the tectonic evolution and geotechnical parameters of the crust—constraints that are important for evaluating earthquake hazards, the distribution and extraction of crustal resources, and the storage of hazardous waste and other crustal engineering applications.

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Garca‐Abdeslem, Juan, and Gordon E. Ness. "Inversion of the power spectrum from magnetic anomalies." GEOPHYSICS 59, no. 3 (March 1994): 391–401. http://dx.doi.org/10.1190/1.1443601.

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We develop methods for the modeling and inversion of the power‐density spectrum from magnetic anomaly data assuming that the crustal magnetic field is caused by an ensemble of vertical‐sided and uniformly magnetized prisms. The solution of the forward problem is achieved in the wavenumber domain, where a synthetic spectrum is given by the product of the mathematical expectations of single‐valued functions that describe depth, thickness, and horizontal dimensions of prisms in the ensemble. We use Gaussian and uniform distributions to describe the ensemble and provide a variety of functions from which different statistical models can be obtained. The solution of the inverse problem is achieved iteratively, starting from an initial set of model parameters. It is based on the ridge‐regression algorithm, and its usefulness is assessed in a number of examples with numeric, synthetic and real data spectra. The methods are first tested on the spectrum obtained from a simple artificial magnetic anomaly and on the artificial spectrum caused by an ensemble of source bodies and are found to be capable of recovering the source parameters. Next, the methods are applied to marine magnetic data from a survey offshore of the Yucatán Peninsula, Mexico. The results of this last application are consistent with the crustal structure observed at Chicxulub hole.

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Lynn, C. Elissa, Frederick A. Cook, and Kevin W. Hall. "Tectonic significance of potential-field anomalies in western Canada: results from the Lithoprobe SNORCLE transect." Canadian Journal of Earth Sciences 42, no. 6 (June 1, 2005): 1239–55. http://dx.doi.org/10.1139/e05-037.

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Potential-field anomalies within the Lithoprobe SNORCLE (Slave Northern Cordillera Lithospheric Evolution) transect area provide geometrical constraints for regional crustal and lithospheric structures, as well as for local anomalies when coupled with subsurface geometry visible on nearly 2500 km of deep seismic reflection and refraction profiles. Areal distribution of gravity and magnetic anomalies permit structures to be projected away from seismic cross sections, and forward modelling provides tests of different interpretations of deep (crustal and upper mantle) density structures. In a key result from modelling, a Paleoproterozoic subduction zone beneath the Wopmay orogen probably consists of high-density rocks, such as eclogite, within the upper mantle. This result supports the concept of moderate- to low-angle intra-lithospheric sutures. On an even larger scale, applications of bandpass and directional filters assist in detecting anomalies according to wavelength or azimuthal orientation and thus provide means to track patterns across structural grain. For example, gravity and magnetic trends that are associated with Precambrian rocks of the Canadian Shield can, in some cases, be followed across much of the Cordillera. This result is consistent with North American Precambrian rocks composing much of the crust in the Cordillera and thus that the addition of "new" lithosphere during Mesozoic early Tertiary accretion has been relatively minor.

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KUDO, Takeshi, and Muneyoshi FURUMOTO. "Characterization of crustal structures by fractal analysis of gravity anomalies." Proceedings of the Japan Academy. Ser. B: Physical and Biological Sciences 74, no. 5 (1998): 69–74. http://dx.doi.org/10.2183/pjab.74.69.

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TAKENAKA, Jun, Masahisa YANAGISAWA, Ryoichi FUJII, and Kazuo SHIBUYA. "Crustal Magnetic Anomalies in the Antarctic Region Detected by MAGSAT." Journal of geomagnetism and geoelectricity 43, no. 6 (1991): 525–38. http://dx.doi.org/10.5636/jgg.43.525.

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Kletetschka, Günther, and James H. Stout. "The origin of magnetic anomalies in lower crustal rocks, Labrador." Geophysical Research Letters 25, no. 2 (January 15, 1998): 199–202. http://dx.doi.org/10.1029/97gl03506.

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Urrutia-Fucugauchi, Jaime, and Jesus Hernan Flores-Ruiz. "Bouguer Gravity Anomalies and Regional Crustal Structure in Central Mexico." International Geology Review 38, no. 2 (February 1996): 176–94. http://dx.doi.org/10.1080/00206819709465330.

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Subrahmanyam, V., K. S. Krishna, I. V. Radhakrishna Murthy, K. V. L. N. S. Sarma, Maria Desa, M. V. Ramana, and K. A. Kamesh Raju. "Gravity anomalies and crustal structure of the Bay of Bengal." Earth and Planetary Science Letters 192, no. 3 (October 2001): 447–56. http://dx.doi.org/10.1016/s0012-821x(01)00469-1.

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Nuñez, E., M. Schimmel, D. Stich, and A. Iglesias. "Crustal Velocity Anomalies in Costa Rica from Ambient Noise Tomography." Pure and Applied Geophysics 177, no. 2 (September 9, 2019): 941–60. http://dx.doi.org/10.1007/s00024-019-02315-z.

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Dubey, C. P., and V. M. Tiwari. "Gravity Anomalies and Crustal Thickness Variations over the Western Ghats." Journal of the Geological Society of India 92, no. 5 (November 2018): 517–22. http://dx.doi.org/10.1007/s12594-018-1059-7.

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Korenaga, Jun, W. Steven Holbrook, Robert S. Detrick, and Peter B. Kelemen. "Gravity anomalies and crustal structure at the southeast Greenland margin." Journal of Geophysical Research: Solid Earth 106, B5 (May 10, 2001): 8853–70. http://dx.doi.org/10.1029/2000jb900416.

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Quesnel, Yoann, Benoit Langlais, and Christophe Sotin. "Local inversion of magnetic anomalies: Implication for Mars’ crustal evolution." Planetary and Space Science 55, no. 3 (February 2007): 258–69. http://dx.doi.org/10.1016/j.pss.2006.02.004.

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Li-Min, WEN, KANG Guo-Fa, BAI Chun-Hua, GAO Guo-Ming, ZHENG An-Ran, and AN Bai-Lin. "CRUSTAL MAGNETIC ANOMALIES AND GEOLOGICAL STRUCTURE IN THE YUNNAN REGION." Chinese Journal of Geophysics 60, no. 6 (November 2017): 613–26. http://dx.doi.org/10.1002/cjg2.30072.

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Pailoplee, Santi. "Mapping b-Value Anomalies Along the Indonesian Island Chain: Implications for Upcoming Earthquakes." Journal of Earthquake and Tsunami 08, no. 04 (October 2014): 1450010. http://dx.doi.org/10.1142/s1793431114500109.

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In this study, the geospatial frequency–magnitude distribution (FMD) b-value images of the prospect sources of upcoming earthquakes were investigated along the Indonesian Sunda Margin (ISM) that strikes parallel to and near the Indonesian Island chain. After enhancing the completeness and stability of the earthquake catalogue, the seismicity data were separated according to their seismotectonic setting into shallow crustal and Intraslab earthquakes. In order to verify the spatial relationship between the b-values and the occurrence of subsequent major earthquakes, the complete shallow crustal seismicity dataset (1980–2005) was truncated into the 1980–2000 sub-dataset. Utilizing the suitable assumption of fixed-number of earthquakes, retrospective tests of both the complete and truncated datasets supported that areas of comparatively low b-values could reasonably be expected to predict likely hypocenters of future earthquakes. As a result, the present-day distributions of b-values derived from the complete (1980–2005) shallow crustal and Intraslab seismicity datasets revealed eight and six earthquake-prone areas, respectively, along the ISM. Since most of these high risk areas proposed here are quite close to the major cities of Indonesia, attention should be paid and mitigation plans should be developed for both seismic and tsunami hazards.

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Salem, Ahmed, Chris Green, Matthew Stewart, and Davide De Lerma. "Inversion of gravity data with isostatic constraints." GEOPHYSICS 79, no. 6 (November 1, 2014): A45—A50. http://dx.doi.org/10.1190/geo2014-0220.1.

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We have developed a simple iterative gravity-inversion approach to map the basement and Moho surfaces of a rift basin simultaneously. Gravity anomalies in rift basins commonly consist of interfering broad, positive crustal-thinning anomalies and narrow, negative sedimentary-basin anomalies. In our model, we assumed that the Moho and basement surfaces are in Airy isostatic equilibrium. An initial plane-layered model was iterated to fit the gravity data. We applied the process to a model in which the inverted basement and Moho surfaces matched the model surfaces well and to a gravity profile across the Kosti Basin in Sudan.

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Perrone, Loredana, Angelo De Santis, Cristoforo Abbattista, Lucilla Alfonsi, Leonardo Amoruso, Marianna Carbone, Claudio Cesaroni, et al. "Ionospheric anomalies detected by ionosonde and possibly related to crustal earthquakes in Greece." Annales Geophysicae 36, no. 2 (March 14, 2018): 361–71. http://dx.doi.org/10.5194/angeo-36-361-2018.

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Abstract. Ionosonde data and crustal earthquakes with magnitude M≥6.0 observed in Greece during the 2003–2015 period were examined to check if the relationships obtained earlier between precursory ionospheric anomalies and earthquakes in Japan and central Italy are also valid for Greek earthquakes. The ionospheric anomalies are identified on the observed variations of the sporadic E-layer parameters (h′Es, foEs) and foF2 at the ionospheric station of Athens. The corresponding empirical relationships between the seismo-ionospheric disturbances and the earthquake magnitude and the epicentral distance are obtained and found to be similar to those previously published for other case studies. The large lead times found for the ionospheric anomalies occurrence may confirm a rather long earthquake preparation period. The possibility of using the relationships obtained for earthquake prediction is finally discussed. Keywords. Ionosphere (Ionospheric disturbances)

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Lee, Sungho, Arushi Saxena, Jung-Hun Song, Junkee Rhie, and Eunseo Choi. "Contributions from lithospheric and upper-mantle heterogeneities to upper crustal seismicity in the Korean Peninsula." Geophysical Journal International 229, no. 2 (December 29, 2021): 1175–92. http://dx.doi.org/10.1093/gji/ggab527.

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SUMMARY The Korean Peninsula (KP), located along the eastern margin of the Eurasian and Amurian plates, has experienced continual earthquakes from small to moderate magnitudes. Various models to explain these earthquakes have been proposed, but the origins of the stress responsible for this region's seismicity remain unclear and debated. This study aims to understand the stress field of this region in terms of the contributions from crustal and upper-mantle heterogeneities imaged via seismic tomography using a series of numerical simulations. A crustal seismic velocity model can determine the crustal thickness and density. Upper-mantle seismic velocity anomalies from a regional tomography model were converted to a temperature field, which can determine the structures (e.g. lithospheric thickness, subducting slabs, their gaps, and stagnant features) and density. The heterogeneities in the crustal and upper mantle governed the buoyancy forces and rheology in our models. The modelled surface topography, mantle flow stress, and orientation of maximum horizontal stress, derived from the variations in the crustal thickness, suggest that model with the lithospheric and upper-mantle heterogeneities is required to improve these modelled quantities. The model with upper-mantle thermal anomalies and east–west compression of approximately 50 MPa developed a stress field consistent with the observed seismicity in the KP. However, the modelled and observed orientations of the maximum horizontal stress agree in the western KP but they are inconsistent in the eastern KP. Our analysis, based on the modelled quantities, suggested that compressional stress and mantle heterogeneities may mainly control the seismicity in the western area. In contrast, we found a clear correlation of the relatively thin lithosphere and strong upper-mantle upwelling with the observed seismicity in the Eastern KP, but it is unclear whether stress, driven by these heterogeneities, directly affects the seismicity of the upper crust.

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Abetov, A. E., and A. N. Uzbekov. "Tectonics and gravity field structure of Central Kazakhstan." Naukovyi Visnyk Natsionalnoho Hirnychoho Universytetu, no. 4 (August 2023): 18–25. http://dx.doi.org/10.33271/nvngu/2023-4/018.

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Purpose. Identification of the nature of the manifestation of tectonic elements of different ages in Central Kazakhstan in gravitational fields based on the results of the calculation of regional, intra-crustal and local transformants. Methodology. Synthesis and analysis of the data on integrated interpretation and modeling of gravitational, geomagnetic, geothermal fields, the latest movements of the Earth’s crust and parameters of the seismic regime, tectonics and stratigraphy of rocks. Findings. Regional, intra-crustal and local heterogeneities in the lithosphere manifest themselves differently in blocks of Precambrian rocks, Early and Late Caledonides, Early and Late Hercynides. They may be associated with the processes of Paleozoic intracontinental rifting, with the rise of mantle matter and its emplacement into the Earth’s crust, followed by the manifestation of Late Paleozoic orogenesis, doubling of the thickness of the Earth’s crust, outpourings of magmatic formations. Originality. It is established that large gravitational minima are distinguished in areas with Hercynian folding, characterized by abnormally high amplitudes in the movement of the Earth’s crust. In the regions of the Caledonian folding, the values of gravity field anomalies of intermediate intensity and increased amplitudes of the latest movements of the Earth’s crust are manifested. Areas with Pre-Paleozoic folding have relative maxima of gravitational anomalies and minimum values of the latest movements of the Earth’s crust. Earthquake sources are concentrated in the consolidated crust at the junction of areas with different ages of basement consolidation, in gradient zones of geothermal, geomagnetic and gravitational anomalies. According to the variations of the intra-crustal transformant, it was found that a wide range of changes in the values of the gravitational field corresponds to areas with minimal temperature values, whereas in areas with increased temperature values, the range of changes in the values of gravity anomalies is reduced. The distribution of the local transformant of the gravitational field indicates the existence of highly variable anomalies, which reflects the high-frequency gravitational effect of near-surface objects of the Earth’s crust. Practical value. The distribution of inhomogeneities in the lithosphere with various density, geomagnetic and geothermal anomalies of geophysical fields, the nature of the seismic regime and the latest movements of the Earth’s crust predetermined the formation of geostructures with different types of mineralization, each of which is recommended to be searched and explored by a specific rational set of geophysical methods.

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Wittpenn, Nancy A., Christopher G. A. Harrison, and David W. Handschumacher. "Crustal magnetization in the South Atlantic from inversion of magnetic anomalies." Journal of Geophysical Research: Solid Earth 94, B11 (November 10, 1989): 15463–80. http://dx.doi.org/10.1029/jb094ib11p15463.

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41

Watts, A. B. "Gravity anomalies, flexure and crustal structure at the Mozambique rifted margin." Marine and Petroleum Geology 18, no. 4 (April 2001): 445–55. http://dx.doi.org/10.1016/s0264-8172(00)00079-9.

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Satya Kumar, A. V., R. P. Rajasekhar, and V. M. Tiwari. "Gravity anomalies and crustal structure of the Lunar far side highlands." Planetary and Space Science 163 (November 2018): 106–13. http://dx.doi.org/10.1016/j.pss.2018.04.009.

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43

Gao, Guoming, Guofa Kang, Chunhua Bai, and Limin Wen. "Study on crustal magnetic anomalies and Curie surface in Southeast Tibet." Journal of Asian Earth Sciences 97 (January 2015): 169–77. http://dx.doi.org/10.1016/j.jseaes.2014.10.035.

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44

H'faiedh, M., J. Dorel, and J. Dubois. "Crustal anomalies under the Tunisian seismograph array using teleseismic P waves." Tectonophysics 118, no. 1-2 (September 1985): 131–41. http://dx.doi.org/10.1016/0040-1951(85)90163-5.

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Barckhausen, Udo, Meike Bagge, and Douglas S. Wilson. "Seafloor spreading anomalies and crustal ages of the Clarion-Clipperton Zone." Marine Geophysical Research 34, no. 2 (June 2013): 79–88. http://dx.doi.org/10.1007/s11001-013-9184-6.

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46

Woodhead, Jon, Janet Hergt, Alan Greig, and Louise Edwards. "Subduction zone Hf-anomalies: Mantle messenger, melting artefact or crustal process?" Earth and Planetary Science Letters 304, no. 1-2 (April 2011): 231–39. http://dx.doi.org/10.1016/j.epsl.2011.01.036.

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47

Suo, Yanhui, Sanzhong Li, Xiyao Li, Lingli Guo, and Yongming Wang. "Crustal thickness anomalies in the Indian Ocean inferred from gravity analysis." Geological Journal 51 (March 8, 2016): 634–43. http://dx.doi.org/10.1002/gj.2786.

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48

Griselin, Mélanie, Nicholas T. Arndt, and W. R. A. Baragar. "Plume–lithosphere interaction and crustal contamination during formation of Coppermine River basalts, Northwest Territories, Canada." Canadian Journal of Earth Sciences 34, no. 7 (July 1, 1997): 958–75. http://dx.doi.org/10.1139/e17-080.

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New trace-element and Nd-isotope analyses were carried out on the Coppermine River basalts, a suite of 1.27 Ga old continental flood basalts in the Northwest Territories of Canada. Although all the samples are tholeiitic basalts, their chemical and isotopic compositions change upwards in the sequence. The lowermost unit has relatively high contents of SiO2 and incompatible trace elements, high ratios of elements with different compatibilities (e.g., Th/Nb, La/Sm), high Gd/Yb, negative Nb anomalies, and low εNd. Samples at the top of the sequence have less pronounced enrichment and fractionation of incompatible elements coupled with an absence of Nb anomalies and positive εNd values. These results are interpreted to indicate that the lavas lowest in the sequence were produced by melting in the garnet stability field, at depths greater than 90 km, and probably in a mantle plume beneath the continental lithosphere. These magmas passed through magma chambers in the lower and upper crust where they became contaminated with crustal rocks. During the course of the eruption of the entire volcanic sequence the extent of crustal contamination became minimal and the lavas lost the chemical signature of residual garnet. The youngest lavas formed by melting in the spinel field and were free of crustal contamination. The site of mantle melting apparently became shallower, perhaps because of lithosphere thinning.

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Okwokwo, Oke I., Neil C. Mitchell, Wen Shi, I. C. F. Stewart, and A. Y. Izzeldin. "How have thick evaporites affected early seafloor spreading magnetic anomalies in the Central Red Sea?" Geophysical Journal International 229, no. 3 (January 21, 2022): 1550–66. http://dx.doi.org/10.1093/gji/ggac012.

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SUMMARY The axial region of the Central Red Sea has been shown to be floored by oceanic crust, but this leaves the low amplitudes of off-axis magnetic anomalies to be explained. Furthermore, if seafloor spreading occurred in the late Miocene, it is unclear how that occurred as widespread evaporites were being deposited then and may have covered the spreading centre. In this study, we derive crustal magnetization for a constant-thickness source layer within the uppermost basement by inverting aeromagnetic anomalies using basement depths derived from seismic reflection and gravity data. Peak-to-trough variations in magnetization away from the axis are found to be slightly less than half of those of normal oceanic crust, but not greatly diminished, and hence the magnetic anomalies are mostly reduced by the greater depth of basement, which is depressed by isostatic loading by the evaporites (kilometres in thickness in places). There is no relationship between seafloor spreading anomalies and the modern distribution of evaporites mapped out using multibeam sonar data; magnetizations are still significant even where the basement lies several kilometres under the evaporites. This suggests that magnetizations have not been more greatly affected by alteration under the evaporites than typically exposed oceanic crust. A prominent magnetization peak commonly occurs at 60–80 km from the axis on both tectonic plates, coinciding with a basement low suggested previously to mark the transition to continental crust closer to the coasts. We suggest an initial burst of volcanism occurred at Chron 5 (at ∼10 Ma) to produce this feature. Furthermore, an abrupt change is found at ∼5 Ma from low-frequency anomalies off-axis to high-frequency anomalies towards the present axis. This potentially represents the stage at which buried spreading centres became exposed. In this interpretation, intrusions such as sills at the buried spreading centre led to broad magnetic anomalies, whereas the later exposure of the spreading centre led to a more typical development of crustal magnetization by rapid cooling of extrusives.

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Koulakov, I., G. Maksotova, S. Mukhopadhyay, J. Raoof, J. R. Kayal, A. Jakovlev, and A. Vasilevsky. "Variations of the crustal thickness in Nepal Himalayas based on tomographic inversion of regional earthquake data." Solid Earth Discussions 6, no. 2 (October 2, 2014): 2867–83. http://dx.doi.org/10.5194/sed-6-2867-2014.

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Abstract. We estimate variations of the crustal thickness beneath the Nepal Himalayas based on tomographic inversion of regional earthquake data. We have obtained a low-velocity anomaly in the upper part of the model down to depths of 40 to 80 km and proposed that the lower limit of this anomaly represents variations of the Moho depth. This statement was supported by results of synthetic modeling. The obtained variations of crustal thickness match fairly well with the free-air gravity anomalies: thinner crust patterns correspond to lower gravity values and vice versa. There is also some correlation with magnetic field: higher magnetic values correspond to the major areas of thicker crust. We propose that elevated magnetic values can be associated with more rigid segments of the incoming Indian crust which cause more compression in the thrust zone and leads to stronger crustal thickening.

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Journal articles on the topic 'Crustal anomalies'

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